Field of the Invention
The present invention provides apparatus, method and system for photothermal treatment of retinal tissue.
Background
Conditions such as diabetic retinopathy and age-related macular degeneration are subject to photocoagulative treatment with laser light. While this type of laser light treatment slows the damage rate of the underlying disease, it has its set of problems. For example, because the treatment entails exposing the eye to a large number of laser light pulses for a long period of time (typically each pulse is on the order of 100 ms or more), damage can be caused to the patient's sensory retina from the heat that is generated. During the treatment, heat is generated predominantly in the retinal pigmented epithelium (RPE), which is the melanin-containing layer of the retina directly beneath the photoreceptors of the sensory retina. Although visible light is predominantly absorbed in the RPE, this type of treatment irreversibly damages the overlying sensory retina and negatively affects the patient's vision. Such long pulses are not required to perform effective treatment, and cause undue patient discomfort and tissue damage. However, most surgical laser systems available today utilize mechanical shutters that require milliseconds to open and close, thus limiting the lower limit of available pulse durations.
Because laser treatment often entails the use of long pulses that could potentially cause damage to the patient's sensory retina, the treatment is often performed with pulses of shorter duration. Turning the laser source on and off directly, however, is neither effective nor cost-efficient because of the optical transients generated and possible damage to the light source. Without the ability to shutter the beam downstream, using a chopper or rotating polygon scanner as a shutter element is not desirable. Because their reliable performance is based upon constant motion, such devices do not provide a convenient and efficient means to adjust the ultimate shape, size and location of the transmitted light.
Today either a slit-lamp-mounted laser delivery device or head mounted laser indirect ophthalmoscope are commonly used for this type of laser light treatment. In the slit lamp device, the slit lamp is arranged to allow easy illumination and microscopic viewing of the eye of a seated patient. Slit lamps used in laser treatment/surgery are a high-brightness forward illuminator and microscope assemblies mounted on a shared pivot point. This arrangement allows the viewing angle of the microscope and illuminator to be changed as often as desired without moving the field of illumination or visualization transversely.
While the most often-used of such devices, slit-lamp-mounted laser delivery devices have their shortcomings. Specifically, certain parts of the eye are difficult to treat with this type of device. For example, the anterior aspect of a retinal break is by far the most important part to seal, as this is the area most subjected to vitreous traction. However, this area is not completely accessible with a slit-lamp-delivered laser system. Also, the slit-lamp-mounted laser delivery device is not well suited for treating small infants or bed-ridden patients. Furthermore, it is difficult to orient the patient's head position with slit-lamp-mounted systems. Thus, these devices have limited ability to treat patients with detached retinas and other conditions where gas or dense fluids have been introduced into the eye to secure detached tissues prior to laser exposure. To treat these conditions, the patient's head is oriented to reposition the tissue or tamponade material.
The laser indirect ophthalmoscope (LIO) may be used in lieu of the slit-lamp-mounted laser delivery device to overcome these shortcomings. The LIO is worn on the physician's head and is used to treat peripheral retinal disorders, particularly in infants or adults requiring treatment in the supine position. It is typically used in an operating room or clinical environment. Traditionally, an LIO is used with a fiber optic to a beam delivery system that is worn by a physician to deliver treatment spots one at a time, with the physician moving their head and/or the objective lens to reposition the aiming beam prior to delivering another spot of treatment light.
An improved technique of pulsed laser treatment is desired. Both of the abovementioned approaches lend themselves to the use of the present invention.